[Amps] Re: PUT your price on your forsale WAS FS:cheap tubesGU74B,GI7B,GS9B,GS23B

[Steve Thompson]

-----Original Message-----
From: yo9fzs <yo9fzs@office.deck.ro>
To: amps@contesting.com <amps@contesting.com>
Date: 13 May 2002 07:11
Subject: Re: [Amps] Re: PUT your price on your forsale WAS FS:cheap
tubesGU74B,GI7B,GS9B,GS23B


>In a previous discussion I wrote about the following possible problem.
>Before using the GI7 and similar tubes to full output, check how the anode
>cooler sit on the flat anode tube surface. I have a GI7 for which the anode
>cooler is making properly thermal contact with the anode flate surface only
>for a very small area surrounding the tube anode screw, and another with
>similar, but less prominent such problem. The anode cooler sitting surface
>it is not flat.
>Put a light source behind the tube an look if the light can be seen between
the
>anode cooler and its sitting tube flat surface.
>You may need to use some sort of heatsink compund there.

If the contact is so bad, I think that heatsink compound will not fix
things. Its thermal conductivity is a little bit better than air, but
nowhere near even poor metal to metal contact. I think that time spent
machining the heatsink would be better.

>And about the heatsink compound, from some time, the heatsinks/coolers
>for the computer CPU's came with another type of compound, made
>(probably) from aluminum powder mixed with some sort of grease.
>It is like a silver grease.

>Is this type of heatsink compound better than the wide used before white
one?

I don't know this type, but I measured copper loaded grease and it was a
little bit better than the white stuff, but got worse when the grease dried
out. Even when wet it was nowhere near as good as good as improving the
surface to surface contact.

Steve

>(other than if it touch some surfaces - like the ceramic it is VERY hard to
>get it clean again!)
>
>73's,
>Traian
>
>
>"Peter Frenning, OZ1PIF" wrote:
>
>> Said Jim:
>> > Max quoted a price of $15. for GI7Bs plus shipping, which is reasonable
>> but
>> > I'm not going to beat his door down.  YMMV, etc.  The anode cooler on
>> these
>> > tubes is not particularly effective for full-output 100% duty-cycle
use,
>> > and it should be replaced for these applications, or the tube derated.
>> > Liquid cooling is a good option.
>>
>> I agree, I agree, but still... I'm using 1 of these (GI7bT variant, same
>> cooler) beasties in my mostly HB 144MHz amp, which has been seeing a LOT
of
>> 100% duty cycle usage lately (WSJT), and other than having to watch the
Ia
>> needle and occasionally adjust the tuning, it has been turning out 300W+
for
>> hours and hours (30s on, 30s off, I had the lid off a few days ago, and
the
>> "hood ornament" had become even more attractive! being colored a nice
>> blue/violet shade along the edges and corners of the fins...
>> The tube still works fine though.
>> I also have to admit the it has indeed run away for me a couple of times:
>> almost no output, 450mA Ia, and glowing a vivid red in the dark! But
again,
>> after cooling down, no apparent ill effects!
>>
>> What it all boils down to: How to get hold of a more suitable anode
cooler
>> thingie? For me liquid cooling is not an option, and I don't have loads
of
>> burnt out tubes to take apart for experimenting with reuse of cooling
>> fins....
>>
>> > the cooler.  The coolers make a nice Christmas tree or hood ornament.
>> They
>> > will also fit nicely on a rettysnitch without further modification.
>> >
>>
>> Vy 73 de OZ1PIF, Peter
>>
>> **********  OZ1PIF **************
>> email: oz1pif(no-spam-filler)@get2net.dk
>> http://hjem.get2net.dk/oz1pif
>> Ph. +45 4619 3239
>> Snailmail:
>> Peter Frenning
>> Ternevej 23
>> DK-4130 Viby Sj.
>> Denmark
>> ***********************************
>>
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